1. Field of the Invention
The present invention relates to a method for cleaning flexible magnetic record discs.
2. Description of the Prior Art
The term magnetic records as used herein refers to those obtained by applying a magnetic coating on one or both surfaces of a flexible, non-magnetic support, such as a polyethylene terephtalate or cellulose triacetate film from 10 to 50 .mu. thick, and thereafter trimming the coated support into a "doughnut" shape having an inside diameter of from 0.5 to 3 cm and an outside diameter of from 10 to 50 cm.
Magnetic records of this type are generally referred to as "floppy" or self-levitating records. In use, the center hole of such a record is placed over the end of and secured to the rotary shaft of a magnetic recording and reproducing device. As the shaft rotates the record horizontally and centrifugally levitates to assume a substantially rigid, planar configuration, whereby magnetic recording and reproduction may be implemented by a magnetic head proximate the surface of the record.
Typically, such records are subject to the phenomenon known as "dropout", which is a rapid reduction in output level for a short period of time due to dust adhering to the surface of the magnetic layer; dropout is particularly pronounced or noticeable in the reproduction of stationary images. It is therefore important to keep the surface of the magnetic layer clean in order to obtain a stable reproduction output.
In order to discuss a widely used prior art cleaning method, a conventional recording and reproducing apparatus for flexible magnetic discs will first be described. Referring to FIG. 1, a recorder/reproducer 1 comprises a base plate 2 having a center hole 3 and an elongated, radial slot 4 spaced from the center hole. A motor 5 disposed below the base plate has a rotary shaft 6 extending through the center hole 3 and protruding above the base plate. A cap 7 is screwed onto the upper end of the shaft 6, and a magnetic head 8 extends up through the slot 4. A magnetic record or disc 9 is arranged so that the surface of a magnetic layer 10 formed on a flexible support 11 is opposite the upper surface of the base plate 2. The upper end of the shaft 6 is inserted into a center hole 9a in the disc, and the cap 7 is screwed onto one shaft to clamp the disc thereto. The motor 5 rotates the shaft 6 in the direction of arrow A at 900 to 3600 r.p.m. to centrifugally levitate the disc 9 with a normal clearance H of from 50 to 2,000 .mu. between the surface of the magnetic layer 10 and the upper surface of the base plate 2. The arrow C designates air drawn up or blown up through the center hole 3, and thrown spirally outwardly in the gap H by centrifugal force due to its frictional adherence to the magnetic layer 10.
To clean the disc, the magnetic head 8 is extended upwardly through the slot 4 until its upper surface comes into contact with the surface of the magnetic layer 10. The head is then moved radially in the direction of arrow B so that the entire recording area of the layer 10 slidably contacts the upper surface of the head 1, whereby harmful dust adhering to the surface of the disc is tranferred onto the upper surface of the head 8 or scraped off thereby to cleam the disc.
This prior art cleaning method suffers from the following disadvantages, however:
(1) Since the entire recording area of the disc is brought into sliding contact with the magnetic head 8 in the cleaning operation, the upper surface of the head 1 is rapidly worn down and its service life is thus materially reduced.
(2) As the upper surface of the head 8 is normally made of a very hard material, the dust induces push-scars, frictional scars, and scoring in the surface of the magnetic layer 10, which degrades the recording and reproducing quality thereof.
(3) The upper surfce of the magnetic head 8 is generally quite narrow, resulting in a low cleaning efficiency.